Traditional two-stage blow molding of plastic hollow articles, typically involve the manufacture of a preform, or parison, the placement of the preform within a split, female mold, and the molding of the preform into its resultant shape under pressure. The preform or parison can be produced in any number of a variety of methods, all of which are well-known. Some examples of common preform production methods include, but are not limited to, extrusion molding, injection molding, compression molding, thermoforming, or various combinations and derivatives of these techniques.
In recent years, multi-layered containers have become popular and widely used in the field of hollow plastic containers. Multi-layered preforms and containers are typically manufactured to allow for the use of different materials in specific layers wherein each material has particular properties adapted to perform a desired function. To make better and more economical use of the various plastic material components, it is often desirable to construct a preform having a comparatively thin inner layer of a generally more expensive first polymer and a comparatively thicker outer layers of less expensive and/or less desirable polymers.
In some applications, a relatively thin inner layer may be used to prevent the intended contents of the final article from direct contact with the outer wall of the container. In other cases, the goal of a certain layer of material may be to provide an additional gas or oxygen barrier in order to reduce the amount or rate of permeation through the walls of the container. The form of layering employed can be tailored to serve multiple purposes and to meet various functional needs.
While various techniques may be applied to manufacture such multi-layered preforms, the present invention is particularly well-suited to processes which incorporate the use of a comparatively thin-walled cylindrical inner liner, or "sleeve," generally having a generally-closed bottom portion and an open neck. Such liners and preforms can be manufactured through a wide variety of processes, including those represented in the following devices and methods.
For example, U.S. Pat. No. 4,109,813 discloses the manufacture of a multi-layered preform which includes the placement of a preformed sleeve over a core in a parison mold and injecting a parison around the core and sleeve within the mold. The disclosure teaches that once the core is inserted into a sleeve, a vacuum may be employed to blow the parison into the final shape and the sleeve will be caused to be pressed against the core so that it will remain attached thereto.
U.S. Pat. No. 5,464,106 discloses a multi-layer preform and container comprised of an inner layer having variable thickness in addition to an outer layer. One specified method of forming the multi-layered preform involves the extrusion (or co-extrusion) of the liner, forming the liner into its final shape via blow molder, and then moving the liner to an injection molder where the outer layer is then formed.
In multi-layer applications such as the foregoing, it is important, and often critical, that the liner remains properly seated on the corresponding core rod prior to the subsequent molding of an outer layer. This is true regardless of whether the outer layer is produced by injection molding, compression molding, or other manufacturing techniques. Therefore, by introducing design enhancements to the physical structure of the liner, the seating of the liner can be improved, and the resultant article will be produced with more efficiency, with improved consistency, and with less variation.